FIG. 10 shows an example of conventional antenna duplexer schematically. The example employs a system having a plurality of antenna duplexers 1 and 2 housed in one package 5, selecting respective antenna duplexers by switch 3. In FIG. 10, switch 3 connects to antenna 4. Antenna duplexer 1 includes transmission terminal Tx1 and reception terminal Rx1 respectively. Antenna duplexer 2 includes similar terminals Tx2 and Rx2 respectively. Another known system (not shown) is to select one of antenna duplexers provided separately using a switching circuit.
A conventional art related to the present invention is disclosed for instance in Japanese Patent Laid-Open Application No. 2000-349586.
In a conventional art, generally, a large overall size of the antenna duplexer must be accepted since a switching circuit and respective antenna duplexers are provided separately. A large current consumption must also be accepted due to the switching circuit provided additionally. Even if the current consumption is restrained to a low level, the problem is that signal distortions such as harmonic components generated in signal transmission or intermodulation generated in signal reception are likely to occur due to a non-linearity of the switching circuit. Additionally, switching circuits or surface acoustic wave (SAW) filters used in the antenna duplexer must accept problems of deterioration in electrical characteristics of the antenna duplexer itself or peripheral circuits due to undesired surge pulses intruding through the antenna terminal. Particularly, switching circuits near the antenna or adjacent circuits are likely to be influenced by the surge pulses, causing in some case the circuits to deteriorate in electrical or physical characteristics.
The present invention can provide an antenna duplexer with a high performance and a high reliability while having a compact size.